Grass Seed Calculator

Grass seed is sold by the pound, but lawns are measured in square feet — and the right rate between the two depends on the grass species and whether you’re starting fresh or thickening what’s already there. Our grass seed calculator above does the conversion instantly, using the seeding rate for your grass type and cutting it in half automatically for overseeding.

The Calculation

Seed needed (lbs) = Lawn area ÷ 1,000 × Seeding rate × Seeding type factor

Seeding rates are always quoted per 1,000 square feet — it’s the industry’s standard unit. A new lawn gets the full rate; overseeding an existing lawn needs roughly half, because you’re filling gaps rather than covering bare soil.

Seeding Rates by Grass Type

The rate varies enormously between species because seed sizes differ — there are about 2 million Kentucky bluegrass seeds in a pound, but only around 230,000 tall fescue seeds:

Grass type	New lawn (lb/1,000 sq ft)	Overseeding
Kentucky bluegrass	2–3	1–1.5
Tall fescue	6–8	3–4
Perennial ryegrass	5–9	2.5–4.5
Fine fescue	4–5	2–2.5
Bermuda (hulled)	1–2	0.5–1
Zoysia	1–2	0.5–1

Enter the rate for your specific mix in the calculator — the bag will state it, and the bag’s number beats any table when they disagree.

More Seed Is Not a Better Lawn

The most common seeding mistake is doubling the rate “to be safe.” It backfires: seedlings sown too densely compete for light, water and nitrogen, grow spindly, and are hit harder by damping-off fungus. You end up with a thinner lawn than if you had seeded correctly. Stay within the recommended range; put the extra money into soil preparation instead — that’s what actually determines success.

Timing Beats Everything

Cool-season grasses (bluegrass, fescue, ryegrass) establish best in late summer to early fall — warm soil, cooling air, fewer weeds. Spring is second-best.

Warm-season grasses (bermuda, zoysia) want late spring to early summer, once soil temperatures pass 65°F (18°C).

Seed thrown down at the wrong time of year mostly feeds the birds. If you’re outside the window, consider waiting — seed stores well for a year in a cool, dry place.

Getting Seed to Actually Grow

• Prep the surface: mow short, rake out debris, and loosen the top quarter-inch of soil. Seed must touch soil, not sit on thatch.
• Spread half the seed in one direction, half at 90° with a broadcast spreader for even coverage.
• Rake lightly and press: seed buried deeper than 1/4 inch won’t emerge; seed lying on the surface dries out. A light raking plus a lawn roller (or foot traffic) gives contact without burial.
• Water lightly, twice daily until germination — the surface should stay damp, never soggy — then gradually shift to deeper, less frequent watering.
• Hold the crabgrass preventer: most pre-emergent herbicides block grass seed too. Skip them for 8+ weeks around seeding.

Frequently Asked Questions

How much seed for 5,000 sq ft of tall fescue? New lawn at 7 lb/1,000: 35 lbs. Overseeding: about 18 lbs.

How long does grass seed take to germinate? Perennial ryegrass 5–10 days, tall fescue 7–14, Kentucky bluegrass a patience-testing 14–30 days. Mixes green up in waves.

Is seed in a “coated” bag different? Coated seed carries a clay/nutrient shell that improves moisture retention — but coating is typically half the bag’s weight. If your bag is coated, effectively double the application rate by weight or follow the bag’s own chart.

When can I mow new grass? When it reaches about 3.5 inches — and make sure the soil is dry enough that the mower doesn’t tear seedlings out.

Estimates are for planning purposes. Rates vary by cultivar and mix — the number printed on your seed bag wins.